Abstract. We present a six-year global climatology of cloud properties, obtained from
observations of the Atmospheric Infrared Sounder (AIRS) onboard the NASA
Aqua satellite. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observations (CALIPSO) combined with CloudSat observations, both missions
launched as part of the A-Train in 2006, provide a unique opportunity to
evaluate the retrieved AIRS cloud properties such as cloud amount and
height. In addition, they permit to explore the vertical structure of
different cloud types. AIRS-LMD cloud detection agrees with CALIPSO about
85% over ocean and about 75% over land. Global cloud amount has been
estimated from 66% to 74%, depending on the weighting of not cloudy AIRS
footprints by partial cloud cover from 0 to 0.3. 42% of all clouds are
high clouds, and about 42% of all clouds are single layer low-level
clouds. The "radiative" cloud height determined by the AIRS-LMD retrieval
corresponds well to the height of the maximum backscatter signal and of the
"apparent middle" of the cloud. Whereas the real cloud thickness of high
opaque clouds often fills the whole troposphere, their "apparent" cloud
thickness (at which optical depth reaches about 5) is on average only 2.5 km.
The real geometrical thickness of optically thin cirrus as identified by
AIRS-LMD is identical to the "apparent" cloud thickness with an average of
about 2.5 km in the tropics and midlatitudes. High clouds in the tropics
have slightly more diffusive cloud tops than at higher latitudes. In
general, the depth of the maximum backscatter signal increases nearly
linearly with increasing "apparent" cloud thickness. For the same
"apparent"
cloud thickness optically thin cirrus show a maximum backscatter about
10% deeper inside the cloud than optically thicker clouds. We also show
that only the geometrically thickest opaque clouds and (the probably
surrounding anvil) cirrus penetrate the stratosphere in the tropics.